DALLAS -- Caron Butler could miss the rest of the season because of a knee injury, a tough blow for the already-ailing Dallas Mavericks.

A person with direct knowledge of the initial diagnosis told ESPNDallas.com's Tim MacMahon that the symptoms indicated Butler suffered at least a partial tear of the patellar tendon in his right knee.

If it is a partial tear, Butler could be out two months. However, if it's a full tear, he would miss the rest of the season. The Mavericks won't be certain about the extent of the injury until they get the results of an MRI that will be taken after Butler returns to Dallas on Sunday.

Butler went down during a loss at Milwaukee on Saturday night. He was coming off a season-high 30-point performance the previous game while picking up the offensive slack because of an injury to leading scorer Dirk Nowitzki.

Nowitzki has a sprained right knee. He is day to day, and Dallas is 0-3 without him.

"We're afraid that it's potentially serious," Dallas coach Rick Carlisle said after Saturday's game. "We'll find out [Sunday] where things are at, probably later in the day."

Butler, a small forward, is the team's third-leading scorer at 15.0 points per game. He plays an average of 30 minutes. The injury could be especially costly to him because he will be a free agent after this season.

Shawn Marion would be a strong option to replace him, but he missed the Bucks game with a thigh contusion.

Rookie Dominique Jones, the Mavericks' first-round pick, will join the team in Cleveland for Sunday's game. Jones had been playing for the Texas Legends, the Mavericks' D-League affiliate, averaging 18.2 points, 5.2 rebounds and 5.0 assists in 10 games.